sub trim;
...
    my ($error) = 0;
    my @other_addresses = map trim, split( /\n/, $email_list );
        foreach (@other_addresses) {
        my $ok = Email::Valid->address($_);
        $error++ if(!$ok);
        print "address($_) = $ok<br>";
        print "error ".$error."<br>";
        }

    $error_message .= "$error Email list contains an invalid email address.<br>" if ($error > 0);

...
sub trim {
   my ($s) = @_;
   for ($s) {
      s/^\s+//;
      s/\s+$//;
      return $_;
   }
}

##</code><code>##

address() =
error 1
address() =
error 2
There was an error with your form submission.

2 Email list contains an invalid email address.